Digi Rabbit 5000, User Manual

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358 Rabbit 5000 Microprocessor User’s Manual
30.3.5 System/User Mode Instructions
Seven instructions exist primarily to support the System/User Mode, and are listed in
Table 30-3. Note that
IDET
shares the value of
LD E,E
in the opcode table, and will
always perform that operation (but will have special behavior when the System/User
Mode is enabled and the processor is in System Mode). In addition, if the ALTD prefix
appears before the instruction,
LD E’,E
is always executed and the special behavior does
not occur.
The processor keeps a one-byte stack (called the SU register) that is analogous to the IP
register that keeps track of the interrupt priority. Every time
SETUSR
is executed (to enter
the User Mode), or an interrupt occurs, or
SYSCALL
or
RST
is executed (to enter System
Mode), the current mode is pushed onto the SU register. When a
SURES
is executed, the
previous mode is popped off the SU register.
Table 30-3. System/User Mode Instructions
Instruction Bytes clk A I S Z V C Operation Priv
SETUSR 2 4 - - - - - SU = {SU[5:0], 0x01} Yes
PUSH SU
2 9 - - - - - (SP-1) = SU; SP = SP - 1 Yes
POP SU
2 7 - - - - - SU = (SP); SP = SP + 1 Yes
SURES
2 4 - - - - - SU = {SU[1:0], SU[7:2]} Yes
IDET 1 2 - - - - -
Performs
LD E,E
, but if
(EDMF && SU[0]) then the System
Violation interrupt flag is set; if ALTD
appears before it always does
LD E’,E
No
RDMODE
2 4 - - - - * CF = SU[0] Yes
SYSCALL
2 10 - - - - -
SP = SP - 2; PC = {R,v} where
v = SYSCALL offset
No
SCALL
2 15 - - - - -
(SP-1) = PCH; (SP-2) = PCL; (SP-3) = SU;
SP = SP - 3; PC = {IIR, 01100000};
SU = {SU[5:0], 00}
No
SRET
2 12 - - - - -
SU = (SP); PCL = (SP+1); PCH = (SP+2);
SP = SP+3
No
SETUSRP mn
4 15 - - - - -
SU = {SU[7:2], 01}, (SP-1) = m;
(SP-2) = n; SP = SP-2
No
SETSYSP mn
4 12 - - - - -
SU = {SU[1:0], SU[7:2]}; tmpl = (SP);
tmph = (SP+1); SP = SP+2;
if {tmp ! = mn} System Violation
No